1. Field of the Invention
This invention related to a mobile communication apparatus, a fixed communication apparatus, a communication system and a communication method, and more particularly, is applicable to a mobile communication apparatus which can be used both in a cellular system which is called Personal Communication Service (PCS) proposed in the United States and a Home Base Station (hereinafter, referred to as a HBS) which corresponds to a base unit of a cordless telephone system for a home or a office.
2. Description of the Related Art
Heretofore, a cellular system called a PCS system has been proposed in the United States. As shown in FIG. 1, this PCS system is roughly composed of a PCS terminal equipment and a plurality of PCS base station apparatuses, and constitutes a broad-band communication system.
The PCS terminal equipments 1A to 1C conduct radio communication with the PCS base station apparatus 2A or 2B in order to conduct in sound communication with general telephones and other portable telephones via a wire circuit and a wireless circuit which are connected to the PCS base station apparatus 2A or 2B.
The PCS base station apparatuses 2A and 2B transmit and receive electric waves by a predetermined radio communication method to mediate calling from the PCS terminal equipment 1A to 1C and the receipt of calls at the PCS terminal equipment 1A through 1C. In addition, the PCS base station apparatuses 2A and 2B regularly transmit the identification signal of their own stations as well as an adjacent station signal which is an identification signal of adjacent PCS base station apparatuses so that the PCS terminal equipment 1A to 1C can identify the base station apparatuses. However, since the PCS base station apparatuses 2A and 2B are different from their own systems even if HBS 4 are located in the vicinity thereof, adjacent base signals concerning the HBS 4 are not transmitted.
Incidentally, service areas 3A and 3B shown in the drawings, show geographical areas which are capable of communicating with the PCS base station apparatuses 2A and 2B. In FIG. 1, since the PCS terminal equipment 1A is located in the service area 3A, the PCS terminal equipment 1A communicates by radio with the PCS base station apparatus 2A. On the other hand, since the PCS terminal equipment 1B is located both in service areas 3A and 3B, the PCS terminal equipment 1B communicates by radio with one of the PCS base station apparatus 2A or 2B. On the other hand, since the PCS terminal equipment 1C is located in the service area 3B, the PCS terminal equipment 1C communicates by radio with the PCS base station apparatus 2B.
On the other hand, the HBS 4 corresponds to a base unit of a cordless telephone system which is set up in a home or office. The HBS 4 enables sound communication between other telephones and the PCS terminal equipment via a wire circuit which is connected to itself, by radio communication with the PCS terminal equipment in the place of the PCS base station apparatus. In other words, the HBS 4 constitutes a cordless telephone system, a closed-band communication system together with the PCS terminal equipment. In such a case, the HBS 4 transmits an identification signal either in a periodic manner or in accordance with the demand from the PCS terminal equipment so that the PCS terminal equipment can identify the HBS 4.
Generally, the telephone charge of the wireless circuit which passes through the PCS base station apparatus is higher than that of the wire circuit. For this purpose, it is considered that a HBS 4 is set up in each home or the like and the HBS 4 is used without using the PCS base station apparatus at home to reduce the telephone charge. There is a possibility that more than one thousand HBS 4 may be located in one service area of the PCS base station apparatus because such HBS 4 are set up in many homes.
Note that, the HBS communication area 5A shown in the drawings, shows a geographical area which is capable of communicating with the HBS 4. This HBS communication area 5A is generally narrow, and may be included in a service area of the PCS base station apparatus as shown in FIG. 1.
Incidentally, the PCS terminal equipment generally moves. When the PCS terminal equipment moves out of the service area of the PCS base station apparatus which is currently communicated as a result of the movement, the PCS terminal equipment should be changed to communicate with another PCS base station apparatus. Generally, the change of such service area is referred to as hand-off.
Here, this hand-off will be explained below. For example, in FIG. 1, a case is considered in which the PCS terminal equipment 1B moves from the inside of the service area 3A of the PCS base station apparatus 2A to the inside of the service area 3B of the PCS base station apparatus 2B. At this time, the PCS terminal equipment 1B cannot communicate with the PCS base station apparatus 2A, so that the communication partner must be changed to the PCS base station apparatus 2B.
In this case, the PCS terminal equipment 1B receives the signal of an adjacent station together with an identification signal of the PCS base station apparatus 2A by receiving a signal which is transmitted from the PCS base station apparatus 2A when the PCS terminal equipment 1B is located in the service area 3A. When the electric wave of the PCS base station apparatus 2A is weakened, the PCS terminal equipment 1B investigates the receiving sensitivity of the PCS base station apparatus 2B which is included in the signal of the adjacent station for the hand-off. While communicating with the PCS base station apparatus 2A, the PCS terminal equipment 1B investigates the receiving sensitivity of the PCS base station apparatus 2B by intermittently receiving the electric wave of the PCS base station apparatus 2B. As a result, when the electric wave of the PCS base station apparatus 2B is sufficiently strong enough to be received, the PCS terminal equipment 1B transmits a hand-off demand to the PCS base station apparatus 2A.
The PCS base station apparatus 2A, which has received this hand-off demand, notifies the controller (not shown) which commands the PCS base station apparatuses 2A and 2B of the generation of the hand-off demand. Then when the controller provides a response, the PCS base station apparatus 2A transmits a hand-off instruction to the PCS terminal equipment 1B. The PCS terminal equipment 1B, which has received this instruction, performs the hand-off from the PCS base station apparatus 2A to the PCS base station apparatus 2B. After performing the hand-off, the PCS terminal equipment 1B confirms that the hand-off can be correctly performed with an identification signal of the PCS base station apparatus 2B which is included in the received signal.
In contrast, for example, when a user who possesses the PCS terminal equipment 1A returns home (that is, when the PCS terminal equipment 1A comes into the HBS communication area 5A), it is required that the PCS terminal equipment 1A is handed-off from the PCS base station apparatus 2A to the HBS 4. Besides, in the same manner, when the user leaves home with the PCS terminal equipment 1A in his hands (that is, the PCS terminal equipment 1A is out of the HBS communication area 5A), it is required that the PCS terminal equipment 1A is handed-off from the HBS 4 to the PCS base station apparatus 2A or 2B.
Incidentally, the PCS base station apparatuses 2A and 2B do not transmit an adjacent station signal with respect to the HBS 4, which is different from its own system. Therefore, when the PCS terminal equipment 1A hands-off, for example, from the PCS base station apparatus 2A to the HBS 4, it is necessary to investigate intermittently whether a signal from the HBS 4 can be received or not during communication with the PCS base station apparatus 2A in order to examine whether hand-off can be performed or not. As a result, when it can be detected that a hand-off can be performed with respect to the HBS 4, the PCS terminal equipment 1A performs a hand-off. After performing the hand-off, the PCS terminal equipment 1A confirms that a hand-off can be correctly performed with an identification signal of the HBS 4 which is included in the received signal.
In this manner, the PCS system performs hand-off control so that the PCS terminal equipments 1A to 1C can move between service areas of the PCS base station apparatuses 2A and 2B. However, such hand-off control that the PCS terminal equipment 1A to 1C can move between the service areas 3A and 3B of the PCS base station apparatuses 2A and 2B and the HBS communication area 5B is not performed. This is because the HBS 4 which is different from its own system is not controlled.
A structure for each of these apparatuses will be explained by using FIGS. 2 and 3. However, for the sake of convenience, a communication system comprising any number of PCS terminal equipments and PCS base station apparatuses is referred to as a PCS communication system. A communication system comprising any number of HBS terminal equipment including the PCS terminal equipment and an HBS is referred to as an HBS communication system.
In the beginning, as shown in FIG. 2, a PCS terminal equipment 1 roughly is comprised of a controller 11 for performing overall control with respect to the sending and receiving of information, a PCS communication part 12 for communicating with the PCS base station apparatus, an HBS communication part 13 for communicating with the HBS 4, a hand-off processing part 14 for performing hand-off process, a switch 15 which is operated by a user, and an antenna 16 for sending and receiving information.
When such PCS terminal equipment 1 communicates with the PCS base station apparatus, the controller 11 controls the PCS communication part 12 in the beginning. The PCS communication part 12, which has received the control, performs appropriate sending and receiving process to the PCS base station apparatus via the antenna 16. On the other hand, in the waiting state, the controller 11 regularly activates the PCS communication part 12 so that a signal from the PCS base station apparatus can be received.
In addition, when the PCS terminal equipment 1 communicates with the HBS 4, the controller 11 controls the HBS communication part 13 in the beginning. The HBS communication part 13, which has received the control, performs appropriate sending and receiving process to the HBS 4 via the antenna 16. On the other hand, in the waiting state, the controller 11 regularly activates the HBS communication part 13 so that a signal from the HBS 4 can be received.
The hand-off processing part 14 grasps a communication partner which is currently in a communication state to perform a hand-off process in accordance with a signal receiving state which is supplied from the controller 11.
For example, when the current communicating system is a PCS communication system, the hand-off process part 14 intermittently monitors the signal receiving state of the HBS 4 to examine whether or not a hand-off can be performed to the HBS communication system. In other words, the hand-off process part 14 suspends the PCS communication part 12 via the controller 11, and activates the HBS communication part 13. The HBS communication part 13 receives the electric waves of the HBS 4 via the antenna 16 to provide the received result to the controller 11. The controller 11, which has received this result, provides to the hand-off process part 14 the signal receiving state showing whether or not the signal of the HBS 4 is being correctly received. The hand-off process part 14 judges whether the signal receiving state of the HBS 4 is in an appropriate range or not. If the state is in the appropriate range, a hand-off is performed from the PCS base station apparatus to the HBS 4 by continuing communication with HBS 4. If the state is not in an appropriate range, the hand-off process part 14 suspends the HBS communication part 13 and activates the PCS communication part 12 again, in order to return to the communication state with the PCS base station apparatus.
On the other hand, when the current communicating system is an HBS communication system, if a signal receiving state obtained via the HBS communication part 13 worsens, the hand-off process part 14 performs a hand-off from the HBS 4 to the PCS base station apparatus when the signal receiving state obtained via the HBS communication part 13 worsens. That is, the hand-off process part 14 suspends the HBS communication part 13 via the controller 11 and activates the PCS communication part 12. The PCS communication part 12 receives the electric wave of the PCS base station apparatus via an antenna 16 and provides the received result to the controller 11. The controller 11, which has received the result, provides a signal receiving state showing whether or not the signal of the PCS base station apparatus is being correctly received to the hand-off process part 14. The hand-off process part 14 judges whether or not the signal receiving state of the PCS base station apparatus is in an appropriate range. If the state is in the appropriate range, the hand-off process part 14 performs a hand-off from the HBS 4 to the PCS base station apparatus by continuing communication with the PCS base station apparatus. If the state is not in an appropriate range, the PCS communication part 12 and the HBS communication part 13 are intermittently operated alternately to perform a hand-off to a system which has accomplished an appropriate receiving operation.
In this manner, the PCS terminal equipment 1 automatically performs a hand-off by monitoring the received state by the hand-off process part 14. In addition, the PCS terminal equipment 1 provides a switch 15 for manual operation. Thereby, a user can directly instruct the start of the hand-off by operating the switch 15. For example, if a user operates this switch 15 when the user that has the PCS terminal equipment 1 returns home or leaves home, the hand-off process part 14 receives this switch operation and starts the hand-off process.
On the other hand, as shown in FIG. 3, the PCS base station device 2 is roughly comprised of a controller 21 for performing an overall control with respect to the sending and receiving of information, a transmitting part 22 for transmitting a signal to the PCS terminal equipment 1, a receiving part 23 for receiving a signal from the PCS terminal equipment 1, a hand-off controller 24 for performing hand-off process, and an antenna 25 for sending and receiving information.
When such PCS base station apparatus 2 communicates PCS terminal equipment 1, the controller 21 controls the transmitting part 22 and the receiving part 23 in the beginning, and activates the transmitting part 22 and the receiving part 23. The transmitting part 22, which has received the control, transmits information obtained from the controller 21 with respect to the PCS terminal equipment 1 in a predetermined communication mode. In addition, the receiving part 23 receives information obtained from the PCS terminal equipment 1 in a predetermined communication mode to provide the information to the controller 21.
The hand-off controller 24 grasps the PCS terminal equipment 1 which is located in its own service area in order to control when the PCS terminal equipment 1 performs a hand-off to another service area. For example, when the PCS terminal equipment 1 which is located in its own service area generates a hand-off demand because the signal receiving state has worsened, the hand-off controller 24 requests a hand-off to another service area of the PCS terminal equipment 1 with respect to the controller (not shown) which commands all the PCS base station apparatuses 2. When receiving a hand-off instruction from the controller as a response, the hand-off controller 24 controls the transmitting part 22 via the controller 21 to transmit a hand-off instruction to the PCS terminal equipment 1. Thereby, the PCS terminal equipment 1 performs a hand-off to another service area.
By the way, when the PCS terminal equipment 1 is about to perform a hand-off to the HBS 4, the hand-off controller 24 does not perform the process even if the hand-off controller 24 receives a hand-off demand from the PCS terminal equipment 1, and it does not provide a hand-off instruction to the PCS terminal equipment 1. This is because the HBS system is different from its own system, as described above, so that the HBS 4 is not controlled.
On the other hand, in general, the controller 21 regularly transmits an identification signal so that the PCS terminal equipment 1, which is located in its own service area, can identify the PCS base station apparatus 2 and transmits an adjacent station signal which is an identification signal of the adjacent PCS base station apparatus 2 for hand-off. However, the controller 21 does not transmit an adjacent station signal with respect to the HBS 4. This is because that the HBS 4 is different from its own system, in the same manner as described above, so that the HBS 4 is not controlled.
For this reason, the PCS terminal equipment 1 regularly searches for the HBS 4 on its own as described above, and performs hand-off to the HBS 4 when the hand-off is possible.
Now, the PCS terminal equipment 1 automatically performs a hand-off from the PCS base station apparatus 2 to the HBS 4 by monitoring the HBS 4 with the hand-off process part 14, as described above. However, at the waiting time, since the PCS terminal equipment 1 monitors the signal receiving state from the HBS 4 in addition to receive a received signal from the PCS base station apparatus 2, so that the HBS communication part 13 as well as the PCS communication part 12 need to be operated frequently though intermittently. Therefore, there is a problem in that the consumed power of the PCS terminal equipment 1 at the time of waiting increases and the usage time of the driving battery is shortened.
In addition, there is a method by which the user operates the switch 15 to perform hand-off by manual operation. However, this method suffers from a drawback in that the communication occasion is lost when the user fails to operate the switch 15. Thus, this method still has a problem in terms of the usage.